Discover the ultra-high temperature “big bubble” of the icy ocean floor

The phase state of water is controlled by the temperature and pressure conditions in which it is located, and when the temperature exceeds the gas-liquid separation temperature at the pressure at which it is located, the liquid water is transformed into gaseous water. At an atmospheric pressure, pure water will gasify at 100 degrees Celsius. In the deep sea floor high-pressure environment, the gasification temperature of sea water can reach several hundred degrees Celsius, then, there is a large amount of ultra-high temperature gaseous water in the deep sea? Zhai Jun, a researcher at the Institute of Oceanography of the Chinese Academy of Sciences, gave the answer.

Inverted lake elevation view taken by discovery ROV deep-sea robot

In the 2018 “Science” scientific research ship deep-sea hydrothermal voyage, using China’s independent research and development of deep-sea in situ Raman spectral probe, the Army task force in the cold sea floor for the first time to observe the existence of gaseous water evidence. On May 28th, the results were published in the Journal of Geophysical Research Letters.

“Sandwich” upside-down lake in the deep-sea hydrothermal zone

Deep-sea hydrothermal system has produced abundant mineral and genetic resources, and is considered to be related to the origin of life, which has long attracted scientific attention.

Phase separation is a process of separation of fluid components in deep-sea hydrothermal systems, which has an important influence on the evolution of hydrothermal fluid chemical components. When the temperature of the fluid exceeds the two-phase separation temperature at its pressure, the gas phase of low density, low salinity and gas-rich components will be separated from the brine phase. However, the temperature drops rapidly as the gas phase rises and spews out the sea floor, making it impossible for the steam phase to remain above the sea floor.

“As we passed the deep-sea hydrothermal zone, a gleaming body of water attracted us. Zhang Xin, a researcher at the Institute of Oceanography of the Chinese Academy of Sciences, told the China Science Daily, “When we got close, we found through the high-definition camera of the ‘Discovery’ ROV deep-sea robot that a large number of ‘mushroom-type’ hydrothermal chimney structures formed an ‘upside-down lake’, which is filled with a large number of gleaming bodies of water.” “

A strong layer of light reflection formed by large differences in temperature and density makes the lake surface of the upside-down lake look as flat as a smooth mirror. The researchers immediately performed Raman spectroscopy and temperature measurements on different layers of water in the upside-down lake.

The measurement results of Raman spectroscopy show that the water body in the inverted lake in this area presents a “sandwich” layering structure, with the high temperature steam phase, the hydrothermal fluid mixed with sea water and the normal sea water phase at the bottom from top to bottom. Temperature measurementdata show that the temperature of the top fluid of the “mushroom-type” structure can reach up to 383.3 degrees Celsius, which is already above the temperature of the phase separation of the region’s 2,180-meter water depth condition – 378.1 degrees Celsius. This further verifies the measurement results of Raman’s spectrum, with gaseous water at the top of the upside-down lake mixed with gas components such as CO2, CH4, H2S and so on.

This is the first time that Chinese scientists have found ultra-high temperature gaseous water in the deep-sea hydrothermal zone.

“Big Bubbles” are stuck in the Bowl.

So why can gaseous water survive on the bottom of the region? This is due to the unique hydrothermal chimney structure of the region.

“Gaseous water is water that reaches its gasification temperature, which is equivalent to a large bubble on the sea floor. But the big bubble doesn’t rise because the gaseous water is covered with a layer of hydrothermal sulphide minerals, which is the equivalent of an inverted bowl, covering the bubble. Zhang Xin explained.

The “mushroom-type” chimney structure forms a semi-enclosed system that isolates overheated high-temperature fluids from the surrounding low-temperature seawater. High-temperature hydrothermal vents slowly diffuse into the seawater through the mirror of the upside-down lake (gas-liquid interface), and this special eruption pattern facilitates the precipitation of hydrothermal sulphides at the edge of the chimney, thereby reducing the impact on the marine environment. The dissolution and transportation of metal elements are controlled by fluid density, so the element distribution and sulphide mineralization process of low-density gas phase and supercritical phase hydrothermal venting systems are significantly different from conventional hydrothermal systems.

At present, the supercritical phase and gas phase hydrothermal injection system is only observed in the hydrothermal region of the mid-ocean ridge, and the gas-phase hydrothermal venting system and the supercritical phase-gas-phase eruption system of the mid-ocean ridge observed in the post-arc hydrothermal region have more stable eruption conditions.

“King Kong Diamond” for Deep Sea Hydrothermal Photos

“In-situ detection of such gas phase hydrothermal venting systems helps to reveal the hydrothermal sulphide mineralization process and their impact on the deep-sea environment of such low-density gas phase hydrothermal venting systems. Zhang Xin said.

Reporters learned that the in situ detection of high temperature hydrothermal vents has been a worldwide technical problem, due to the harsh high temperature, high pressure, strong acid (alkali) and turbid fluid environment, deep-sea hot hydrothermal vents have been considered as the optical lens of the no-go zone.

This significant discovery was made thanks to the application of the first deep-sea-based Raman spectral probe directly inserted into the deep-sea hydrothermal vent at 450 degrees Celsius. This Raman spectral probe successfully breaks through the technical bottlenecks such as the intolerant high temperature of ordinary optical lenses and poor particle attachment performance, and provides the first multi-parameter in situ optical detection sensor for the study of the geochemical properties of deep-sea hydrothermal fluids, and provides a new method for studying the effects of hydrothermal fluids on the marine environment and global changes.

By Liao Yang, Correspondent Wang Min